Vascular plugs, or occluders, are well known for occluding bodily vessels and are produced in a variety of forms. They may act to create substantially instantaneous occlusion of a vessel, in which case the structure of the plug provides an impermeable barrier to fluid, or they may act to occlude the vessel over time, in which case the plug will generally have a pervious membrane designed to slow the flow of blood through the vessel. The membrane promotes thrombosis of the blood and eventual occlusion of the vessel by the formed thrombus.
Vascular plugs are typically deployed endoluminally through the patient's vasculature up to the intended site of treatment. For this purpose, it is important to be able to compress the vascular plug radially so as to fit within an introducer assembly of a diameter which can pass readily through the patient's vasculature. To this end, it is known to have vascular occluders which are able to be pulled to an elongate form, which minimizes their lateral dimension and thus enables them to be deployed through catheters of very small diameter. While such designs of plug can optimize the delivery of the plug through the patient's vasculature, particularly where this is tortuous and/or narrow, a plug which expands from an elongate form to a shorter form cannot be positioned precisely in a patient's vessel, which can make such designs unsuitable when the treatment site is short, for example between closely located branch vessels and so on.
Vascular plugs also generally have specific operating diameters, designed to ensure occlusion as well as reliable fixation to the vessel wall so as to minimise the risk of migration of the plug over time. These plugs, however, are vessel-size specific and it is therefore necessary to determine vessel size accurately before treatment, as well as to have available for use a stock of different size plugs. Even with selection of a plug of the correct size, changes in the dimensions or shape of a vessel over time can cause imprecise occlusion and risk of migration of the plug.
Known designs of vascular plug can be found, for example, in US-2012/0,046,687, US-2010/0,179,583, US-2009/0,275,978, WO-01/17,435 and EP-0,664,107.